class QOpcUaClient#

QOpcUaClient allows interaction with an OPC UA server. More…

Inheritance diagram of PySide6.QtOpcUa.QOpcUaClient

Synopsis#

Properties#

  • errorᅟ - Specifies the current error state of the client

  • stateᅟ - Specifies the current connection state of the client

Methods#

Signals#

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description#

QOpcUaClient#

QOpcUaClient implements basic client capabilities to communicate with OPC UA enabled devices and applications. This includes querying a discovery server for known servers, requesting a list of endpoints from a server, connecting and disconnecting.

After successfully connecting to a server, QOpcUaClient allows getting QOpcUaNode objects which enable further interaction with nodes on the OPC UA server. For operations that concern multiple nodes, QOpcUaClient offers an API which supports reading multiple attributes of multiple nodes in a single request to the server.

QOpcUaClient also keeps a local copy of the server’s namespace array which is created after a successful connect. This information can be queried or updated while the connection lasts. The copy of the namespace array is also used for the resolution of expanded node ids and the creation of qualified names from a namespace URI.

Addressing Nodes#

For an introduction to nodes and node ids, see QOpcUaNode .

Usage#

Create a QOpcUaClient using QOpcUaProvider , request a list of endpoints from the server using requestEndpoints and call connectToEndpoint() to connect to one of the available endpoints. After the connection is established, a QOpcUaNode object for the root node is requested.

QOpcUaProvider provider;
if (provider.availableBackends().isEmpty())
    return;
QOpcUaClient *client = provider.createClient(provider.availableBackends()[0]);
if (!client)
    return;
// Connect to the stateChanged signal. Compatible slots of QObjects can be used instead of a lambda.
QObject::connect(client, &QOpcUaClient::stateChanged, [client](QOpcUaClient::ClientState state) {
    qDebug() << "Client state changed:" << state;
    if (state == QOpcUaClient::ClientState::Connected) {
        QOpcUaNode *node = client->node("ns=0;i=84");
        if (node)
            qDebug() << "A node object has been created";
    }
});

QObject::connect(client, &QOpcUaClient::endpointsRequestFinished,
                 [client](QList<QOpcUaEndpointDescription> endpoints) {
    qDebug() << "Endpoints returned:" << endpoints.count();
    if (endpoints.size())
        client->connectToEndpoint(endpoints.first()); // Connect to the first endpoint in the list
});

client->requestEndpoints(QUrl("opc.tcp://127.0.0.1:4840")); // Request a list of endpoints from the server
class ClientState#

This enum type specifies the connection state of the client.

Constant

Description

QOpcUaClient.Disconnected

The client is not connected to a server.

QOpcUaClient.Connecting

The client is currently connecting to a server.

QOpcUaClient.Connected

The client is connected to a server.

QOpcUaClient.Closing

The client has been connected and requests a disconnect from the server.
class ClientError#

This enum type specifies the current error state of the client.

Constant

Description

QOpcUaClient.NoError

No error occurred.

QOpcUaClient.InvalidUrl

The url to connect to has been wrongly specified or a connection to this url failed.

QOpcUaClient.AccessDenied

An attempt to connect to a server using username/password failed due to wrong credentials.

QOpcUaClient.ConnectionError

An error occurred with the connection.

QOpcUaClient.UnknownError

An unknown error occurred.

QOpcUaClient.UnsupportedAuthenticationInformation

The given type or data of authentication information is not supported.

Note

Properties can be used directly when from __feature__ import true_property is used or via accessor functions otherwise.

property errorᅟ: QOpcUaClient.ClientError#

This property Specifies the current error state of the client..

Access functions:
property stateᅟ: QOpcUaClient.ClientState#

This property Specifies the current connection state of the client..

Access functions:
addNode(nodeToAdd)#
Parameters:

nodeToAdd – QOpcUaAddNodeItem

Return type:

bool

Adds the node described by nodeToAdd on the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the addNodeFinished() signal.

The following example code adds new a Variable node on the server:

QOpcUaNodeCreationAttributes attributes;
attributes.setDisplayName(QOpcUaLocalizedText("en", "My new Variable node"));
attributes.setDescription(QOpcUaLocalizedText("en", "A node which has been added at runtime"));
attributes.setValue(23.0, QOpcUa::Types::Double);
attributes.setDataTypeId(QOpcUa::ns0ID(QOpcUa::NodeIds::Namespace0::Double));
attributes.setValueRank(-2); // Scalar or array
attributes.setAccessLevel(QOpcUa::AccessLevelBit::CurrentRead);
attributes.setUserAccessLevel(QOpcUa::AccessLevelBit::CurrentRead);

QOpcUaAddNodeItem item;
item.setParentNodeId(QOpcUaExpandedNodeId("ns=3;s=TestFolder"));
item.setReferenceTypeId(QOpcUa::nodeIdFromReferenceType(QOpcUa::ReferenceTypeId::Organizes));
item.setRequestedNewNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setBrowseName(QOpcUaQualifiedName(3, "MyNewVariableNode"));
item.setNodeClass(QOpcUa::NodeClass::Variable);
item.setNodeAttributes(attributes);

m_client->addNode(item);

See also

deleteNode() addNodeFinished() QOpcUaAddNodeItem

addNodeFinished(requestedNodeId, assignedNodeId, statusCode)#
Parameters:

This signal is emitted after an addNode() operation has finished. requestedNodeId is the requested node id from the addNode() call, assignedNodeId is the node id the server has assigned to the new node. statusCode contains the result of the operation. If the result is Bad , assignedNodeId is empty and no node has been added to the server’s address space.

addReference(referenceToAdd)#
Parameters:

referenceToAdd – QOpcUaAddReferenceItem

Return type:

bool

Adds the reference described by referenceToAdd to the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the addReferenceFinished() signal.

The following example code adds a reference to a node to the “Objects” folder:

QOpcUaAddReferenceItem item;
item.setSourceNodeId(QOpcUa::namespace0Id(QOpcUa::NodeIds::Namespace0::ObjectsFolder));
item.setReferenceTypeId(QOpcUa::nodeIdFromInteger(0, static_cast<quint32>(QOpcUa::ReferenceTypeId::Organizes)));
item.setIsForwardReference(true);
item.setTargetNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setTargetNodeClass(QOpcUa::NodeClass::Variable);

m_client->addReference(item);

See also

deleteReference() addReferenceFinished() QOpcUaAddReferenceItem

addReferenceFinished(sourceNodeId, referenceTypeId, targetNodeId, isForwardReference, statusCode)#
Parameters:

This signal is emitted after an addReference() operation has finished. sourceNodeId, referenceTypeId, targetNodeId and isForwardReference are the values from the addReference() call. statusCode contains the result of the operation.

applicationIdentity()#
Return type:

QOpcUaApplicationIdentity

Returns the application identity of this QOpcUaClient instance.

authenticationInformation()#
Return type:

QOpcUaAuthenticationInformation

Returns the current authentication information.

backend()#
Return type:

str

Returns the name of the backend used by this instance of QOpcUaClient , e.g. “open62541”.

connectError(errorState)#
Parameters:

errorState – QOpcUaErrorState

This signal is emitted when an error happened during connection establishment. The parameter errorState contains information about the error.

In case of client side errors, these can be ignored by calling setIgnoreError on the object.

During execution of a slot connected to this signal the backend is stopped and waits for all slots to return. This allows to pop up a user dialog to ask the enduser for example if to trust an unknown certificate before the backend continues.

connectToEndpoint(endpoint)#
Parameters:

endpoint – QOpcUaEndpointDescription

Connects to the OPC UA endpoint given in endpoint.

QEndpointDescription endpointDescription;
...
client->connectToEndpoint(endpointDescription);

A list of available endpoints is usually obtained by calling requestEndpoints() .

If the endpoint requires username authentication, at least a user name must be set in QOpcUaAuthenticationInformation . Calling this function before setting an authentication information will use the anonymous authentication.

QOpcUaAuthenticationInformation authInfo;
authInfo.setUsernameAuthentication("user", "password");

client->setAuthenticationInformation(authInfo);

See also

connected() stateChanged() setAuthenticationInformation() QOpcUaEndpointDescription

connected()#

This signal is emitted when a connection has been established.

connectionSettings()#
Return type:

QOpcUaConnectionSettings

Returns the connection settings for this client.

deleteNode(nodeId[, deleteTargetReferences=true])#
Parameters:

  • nodeId – str

  • deleteTargetReferences – bool

Return type:

bool

Deletes the node with node id nodeId from the server. If deleteTargetReferences is false, only the references with source node nodeId are deleted. If deleteTargetReferences is true, references with nodeId as target are deleted too.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the deleteNodeFinished() signal.

The following example code deletes a node and all references to it from the server:

m_client->deleteNode(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"), true);

See also

addNode() deleteNodeFinished()

deleteNodeFinished(nodeId, statusCode)#
Parameters:

This signal is emitted after a deleteNode() operation has finished. nodeId is the node id from the deleteNode() call. statusCode contains the result of the operation.

deleteReference(referenceToDelete)#
Parameters:

referenceToDelete – QOpcUaDeleteReferenceItem

Return type:

bool

Deletes the reference described by referenceToDelete from the server.

Returns true if the asynchronous call has been successfully dispatched.

The success of the operation is returned in the deleteReferenceFinished() signal.

The following example code deletes a reference to a node from the “Objects” folder:

QOpcUaDeleteReferenceItem item;
item.setSourceNodeId(QOpcUa::namespace0Id(QOpcUa::NodeIds::Namespace0::ObjectsFolder));
item.setReferenceTypeId(QOpcUa::nodeIdFromInteger(0, static_cast<quint32>(QOpcUa::ReferenceTypeId::Organizes)));
item.setIsForwardReference(true);
item.setTargetNodeId(QOpcUaExpandedNodeId("ns=3;s=MyNewVariableNode"));
item.setDeleteBidirectional(true);

m_client->deleteReference(item);

See also

addReference() deleteReferenceFinished() QOpcUaDeleteReferenceItem

deleteReferenceFinished(sourceNodeId, referenceTypeId, targetNodeId, isForwardReference, statusCode)#
Parameters:

This signal is emitted after a deleteReference() operation has finished. sourceNodeId, referenceTypeId, targetNodeId and isForwardReference are the values from the deleteReference() call. statusCode contains the result of the operation.

disconnectFromEndpoint()#

Disconnects from the server.

disconnected()#

This signal is emitted when a connection has been closed following to a close request.

endpoint()#
Return type:

QOpcUaEndpointDescription

Returns the description of the endpoint the client is currently connected to or was last connected to.

endpointsRequestFinished(endpoints, statusCode, requestUrl)#
Parameters:

  • endpoints – .list of QOpcUaEndpointDescription

  • statusCode – UaStatusCode

  • requestUrl – QUrl

This signal is emitted after a requestEndpoints() operation has finished. statusCode contains the result of the operation. If the result is Good , endpoints contains the descriptions of all endpoints that are available on the server. requestUrl contains the URL that was used in the requestEndpoints() call.

error()#
Return type:

ClientError

Returns the current error state of the client.

Getter of property errorᅟ .

errorChanged(error)#
Parameters:

error – ClientError

Notification signal of property errorᅟ .

findServers(url[, localeIds=list()[, serverUris=list()]])#
Parameters:

  • url – QUrl

  • localeIds – list of strings

  • serverUris – list of strings

Return type:

bool

Starts an asynchronous FindServers request to read a list of known servers from a server or discovery server at url. Returns true if the asynchronous call has been successfully dispatched.

localeIds can be used to select the language of the application names returned by the request. The format is specified in OPC UA 1.05 part 3, 8.4, for example “en” for English, or “de-DE” for German (Germany). If more than one locale ID is specified, the server uses the first match. If there is no match or localeIds is empty, a default locale is chosen by the server.

serverUris may be used to restrict the results to servers with a matching applicationUri in their application description. For example, finding the current URL of the server with the applicationUri “MyPLC”, the following call can be used:

client->findServers(discoveryServerUrl, QStringList(), QStringList({"MyPLC"}));

The results are returned in the findServersFinished() signal.

findServersFinished(servers, statusCode, requestUrl)#
Parameters:

  • servers – .list of QOpcUaApplicationDescription

  • statusCode – UaStatusCode

  • requestUrl – QUrl

This signal is emitted after a findServers() operation has finished. statusCode contains the result of the operation. If the result is Good , servers contains the application descriptions of all servers known to the queried server that matched the filter criteria. requestUrl contains the URL that was used in the findServers() call.

isNamespaceAutoupdateEnabled()#
Return type:

bool

Returns whether autoupdate of the namespace array is enabled.

namespaceArray()#
Return type:

list of strings

Returns the cached value of the namespace array.

The value is only valid after the namespaceArrayUpdated() signal has been emitted.

namespaceArrayChanged(namespaces)#
Parameters:

namespaces – list of strings

This signal is emitted after the namespace array has changed. namespaces contains the content of the server’s namespace table. The index of an entry in namespaces corresponds to the namespace index used in the node id.

namespaceArrayUpdated(namespaces)#
Parameters:

namespaces – list of strings

This signal is emitted after an updateNamespaceArray operation has finished. namespaces contains the content of the server’s namespace table. The index of an entry in namespaces corresponds to the namespace index used in the node id.

If the namespace array content stays the same after the update this signal is emitted nevertheless.

namespaceAutoupdateInterval()#
Return type:

int

Returns the current revised update interval of the namespace array.

See also

setNamespaceAutoupdateInterval(int interval)

node(nodeId)#
Parameters:

nodeId – str

Return type:

QOpcUaNode

Returns a QOpcUaNode object associated with the OPC UA node identified by nodeId. The caller becomes owner of the node object.

If the client is not connected, nullptr is returned. The backends may also return nullptr for other error cases (for example for a malformed node id).

node(expandedNodeId)
Parameters:

expandedNodeId – QOpcUaExpandedNodeId

Return type:

QOpcUaNode

Returns a QOpcUaNode object associated with the OPC UA node identified by expandedNodeId. The caller becomes owner of the node object.

If the node is not on the currently connected server, the namespace can’t be resolved, the node id is malformed or the client is not connected, nullptr is returned.

passwordForPrivateKeyRequired(keyFilePath, password, previousTryWasInvalid)#
Parameters:

  • keyFilePath – str

  • password – str

  • previousTryWasInvalid – bool

This signal is emitted when a password for an encrypted private key is required. The parameter keyFilePath contains the file path to key which is used. The parameter previousTryWasInvalid is true if a previous try to decrypt the key failed (aka invalid password). The parameter password points to a QString that has to be filled with the actual password for the key. In case the previous try failed it contains the previously used password.

During execution of a slot connected to this signal the backend is stopped and waits for all slots to return. This allows to pop up a user dialog to ask the enduser for the password.

pkiConfiguration()#
Return type:

QOpcUaPkiConfiguration

Returns the application’s PKI configuration of this QOpcUaClient instance.

qualifiedNameFromNamespaceUri(namespaceUri, name[, ok=None])#
Parameters:

  • namespaceUri – str

  • name – str

  • ok – bool

Return type:

QOpcUaQualifiedName

Attempts to create a qualified name from namespaceUri and the name string name. Returns the resulting qualified name. An empty qualified name is returned if namespaceUri can’t be resolved.

ok will be set to true if the namespace URI resolution has been successful. If the namespace URI could not be resolved, ok will be set to false.

readHistoryData(request)#
Parameters:

request – QOpcUaHistoryReadRawRequest

Return type:

QOpcUaHistoryReadResponse

Starts a read raw history request for one or multiple nodes. This is the Qt OPC UA representation for the OPC UA ReadHistory service for reading raw historical data defined in OPC UA 1.05 part 4, 5.10.3 .

The start timestamp, end timestamp, number of values per node, returnBounds and nodes to read can be specified in a QOpcUaHistoryReadRawRequest .

Returns a QOpcUaHistoryReadResponse which contains the state of the request if the asynchronous request has been successfully dispatched. The results are returned in the UaStatusCode serviceResult) signal.

In the following example, the historic data from the last two days of two nodes are requested and printed. The result is limited to ten values per node.

QOpcUaHistoryReadRawRequest request(
            { QOpcUaReadItem("ns=1;s=myValue1"), QOpcUaReadItem("ns=1;s=myValue2") },
            QDateTime::currentDateTime(),
            QDateTime::currentDateTime().addDays(-2),
            10,
            true);

QOpcUaHistoryReadResponse *response = m_client->readHistoryData(request);
if (response) {
   QObject::connect(response, &QOpcUaHistoryReadResponse::readHistoryDataFinished,
                    [] (QList<QOpcUaHistoryData> results, QOpcUa::UaStatusCode serviceResult) {
                        if (serviceResult != QOpcUa::UaStatusCode::Good) {
                            qWarning() << "Fetching historical data failed with:" << serviceResult;
                        } else {
                            for (const auto& result : results) {
                                qInfo() << "NodeId:" << result.nodeId();
                                for (const auto &dataValue : result.result())
                                    qInfo() << "Value:" << dataValue.value();
                            }
                        }
                    });
}
readNodeAttributes(nodesToRead)#
Parameters:

nodesToRead – .list of QOpcUaReadItem

Return type:

bool

Starts a read of multiple attributes on different nodes. The node id, the attribute and an index range can be specified for every entry in nodesToRead.

Returns true if the asynchronous request has been successfully dispatched. The results are returned in the readNodeAttributesFinished() signal.

This read function offers an alternative way to read attributes of nodes which can be used for scenarios where the values of a large number of node attributes on different nodes must be read without requiring the other features of the QOpcUaNode based API like monitoring for value changes. All read items in the request are sent to the server in a single request and are answered in a single response which generates a single readNodeAttributesFinished() signal. This reduces the network overhead and the number of signal slot connections if many different nodes are involved.

In the following example, the display name attribute and the two index ranges “0:2” and “5:7” of the value attribute of the same node and the entire value attribute of a second node are read using a single service call:

QList<QOpcUaReadItem> request;
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::DisplayName));
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::Value, "0:2"));
request.push_back(QOpcUaReadItem("ns=1;s=MyArrayNode",
                                 QOpcUa::NodeAttribute::Value, "5:7"));
request.push_back(QOpcUaReadItem("ns=1;s=MyScalarNode));
m_client->readNodeAttributes(request);

See also

QOpcUaReadItem readNodeAttributesFinished()

readNodeAttributesFinished(results, serviceResult)#
Parameters:

  • results – .list of QOpcUaReadResult

  • serviceResult – UaStatusCode

This signal is emitted after a readNodeAttributes() operation has finished.

The elements in results have the same order as the elements in the request. For each requested element, there is a value together with timestamps and the status code in results. serviceResult contains the status code from the OPC UA Read service.

registerNodes(nodesToRegister)#
Parameters:

nodesToRegister – list of strings

Return type:

bool

Registers the node ids in nodesToRegister on the server and returns true if the request has been successfully dispatched. The results are returned in the registerNodesFinished() signal.

The node registration service is used to let the server know that a node will be accessed frequently so it may perform operations like keeping the connection to an external resource open. The server may also return an alias node id which is recommended to be numeric. This might come in handy if a node with a long string identifier node id is used in many requests. The real performance gain (if any) depends on the server’s implementation.

The registered node ids are only guaranteed to be valid for the current session. Any registrations that are no longer needed should be unregistered as soon as possible so the server may free the associated resources.

registerNodesFinished(nodesToRegister, registeredNodeIds, statusCode)#
Parameters:

  • nodesToRegister – list of strings

  • registeredNodeIds – list of strings

  • statusCode – UaStatusCode

This signal is emitted after a registerNodes() operation has finished. nodesToRegister contains the node ids from the request for correlation purposes. The node ids returned by the server are in registeredNodeIds and have the same ordering as the ids in the request. statusCode indicates if the operation was successful.

See also

registerNodes()

requestEndpoints(url)#
Parameters:

url – QUrl

Return type:

bool

Starts an asynchronous GetEndpoints request to read a list of available endpoints from the server at url. Returns true if the asynchronous call has been successfully dispatched.

The endpoint information is returned in the endpointsRequestFinished() signal.

resolveExpandedNodeId(expandedNodeId[, ok=None])#
Parameters:
Return type:

str

Attempts to resolve expandedNodeId to a node id string with numeric namespace index. Returns the node id string if the conversion was successful.

An empty string is returned if the namespace index can’t be resolved or if the identifier part of the expanded node id is malformed. ok will be set to true if the conversion has been successful. If the expanded node id could not be resolved, ok will be set to false.

setApplicationIdentity(identity)#
Parameters:

identity – QOpcUaApplicationIdentity

Sets the application identity for this QOpcUaClient instance to identity.

setAuthenticationInformation(authenticationInformation)#
Parameters:

authenticationInformation – QOpcUaAuthenticationInformation

Sets the authentication information of this client to authenticationInformation.

setConnectionSettings(connectionSettings)#
Parameters:

connectionSettings – QOpcUaConnectionSettings

Sets the connection settings for this client to connectionSettings.

Example:

QOpcUaConnectionSettings settings;
// Ask the server to give localized texts in german with french as fallback
settings.setSessionLocaleIds({ "de", "fr" });
// We need to call some long running methods, increase the request timeout
settings.setRequestTimeout(std::chrono::minutes(2));
opcuaClient->setConnectionSettings(settings);

The values from connectionSettings are applied to any new connections after this point.

setNamespaceAutoupdate(isEnabled)#
Parameters:

isEnabled – bool

Enables automatic update of the namespace table.

Enabling this will keep the local copy of the namespace table updated automatically. namespaceArrayUpdated will be emitted when the array changed. isEnabled determines if autoupdate is being enabled or disabled.

A subscription will be made on the node on the server to keep track of changes. In case a server does not support subscriptions this will not work and isNamespaceAutoupdateEnabled returns false.

setNamespaceAutoupdateInterval(interval)#
Parameters:

interval – int

Sets the interval for the namespace table subscription.

The subscription may be revised by the server.

interval determines the interval to check for changes in milliseconds. The default is once per second.

See also

namespaceAutoupdateInterval() setNamespaceAutoupdate(bool isEnabled)

setPkiConfiguration(config)#
Parameters:

config – QOpcUaPkiConfiguration

Sets the application PKI configuration for this QOpcUaClient instance to config.

state()#
Return type:

ClientState

Getter of property stateᅟ .

stateChanged(state)#
Parameters:

state – ClientState

Notification signal of property stateᅟ .

supportedSecurityPolicies()#
Return type:

list of strings

Returns the security policies supported by the used backend.

This function is currently available as a Technology Preview, and therefore the API and functionality provided by the function may be subject to change at any time without prior notice.

supportedUserTokenTypes()#
Return type:

.list of QOpcUaUserTokenPolicy.TokenType

Returns the user token types supported by the used backend.

This function is currently available as a Technology Preview, and therefore the API and functionality provided by the function may be subject to change at any time without prior notice.

See also

TokenType

unregisterNodes(nodesToUnregister)#
Parameters:

nodesToUnregister – list of strings

Return type:

bool

Unregisters the node ids in nodesToUnregister on the server and returns true if the request has been successfully dispatched. The results are returned in the unregisterNodesFinished() signal.

The node ids to pass in nodesToUnregister must have been obtained via registerNodes() .

See also

registerNodes()

unregisterNodesFinished(nodesToUnregister, statusCode)#
Parameters:

  • nodesToUnregister – list of strings

  • statusCode – UaStatusCode

This signal is emitted after a unregisterNodes() operation has finished. nodesToUnregister contains the node ids from the request for correlation purposes. statusCode indicates if the operation was successful.

updateNamespaceArray()#
Return type:

bool

Requests an update of the namespace array from the server. Returns true if the operation has been successfully dispatched.

The namespaceArrayUpdated() signal is emitted after the operation is finished.

writeNodeAttributes(nodesToWrite)#
Parameters:

nodesToWrite – .list of QOpcUaWriteItem

Return type:

bool

Starts a write for multiple attributes on different nodes. The node id, the attribute, the value, the value type and an index range can be specified for every entry in nodesToWrite.

Returns true if the asynchronous request has been successfully dispatched. The results are returned in the writeNodeAttributesFinished() signal.

This write function offers an alternative way to write attributes of nodes which can be used for scenarios where the values of a large number of node attributes on different nodes must be written without requiring the other features of the QOpcUaNode based API like monitoring for value changes. All write items in the request are sent to the server in a single request and are answered in a single response which generates a single writeNodeAttributesFinished() signal. This reduces the network overhead and the number of signal slot connections if many different nodes are involved.

In the following example, the Values attributes of two different nodes are written in one call. The second node has an array value of which only the first two elements are overwritten:

QList<QOpcUaWriteItem> request;

request.append(QOpcUaWriteItem("ns=2;s=Demo.Static.Scalar.Double", QOpcUa::NodeAttribute::Value,
                                  23.0, QOpcUa::Types::Double));
request.append(QOpcUaWriteItem("ns=2;s=Demo.Static.Arrays.UInt32", QOpcUa::NodeAttribute::Value,
                                  QVariantList({0, 1, 2}), QOpcUa::Types::UInt32, "0:2"));

m_client->writeNodeAttributes(request);

See also

QOpcUaWriteItem writeNodeAttributesFinished()

writeNodeAttributesFinished(results, serviceResult)#
Parameters:

  • results – .list of QOpcUaWriteResult

  • serviceResult – UaStatusCode

This signal is emitted after a writeNodeAttributes() operation has finished.

The elements in results have the same order as the elements in the write request. They contain the value, timestamps and status code received from the server as well as the node id, attribute and index range from the write item. This facilitates matching the result with the request.

serviceResult is the status code from the the OPC UA Write service. If serviceResult is not Good , the entries in results also have an invalid status code and must not be used.